2017 ASHS Annual Conference

Following the completion of eco-dormancy, tart cherry (Prunus cerasus) ‘Montmorency’ pistils steadily lose freeze resistance. Reproductive buds are classified by discrete phenology stages between dormancy and anthesis, each stage associated with a distinct critical survival temperature. Phenology stages, however, have not been correlated with pistil growth and can be difficult to distinguish, especially during early stages of development (dormancy to bud swelling and side green to green tip). Collection of accurate phenotyping data could facilitate the development of predictive models with practical implications for frost protection. Hence, reproductive buds were collected several times per week near the end of eco-dormancy until anthesis. Buds were weighed, imaged using a stereo microscope equipped with a camera, then oven-dried to constant weight. Pistils were extracted from a subset of fresh buds, imaged and measured using image analysis software. The lethal temperature (LT₅₀) of flowers was also determined by a combination of differential thermal analysis (DTA, between dormancy and first swell) and visual observation of oxidative browning (between first swell and anthesis) following freezing at a rate of 1.5°C per hour. The LT₅₀ of tart cherry buds was approximately 1°C higher than previously published data at most phenology stages. Between dormancy and side green, pistil volume increased nearly 7-fold and RWC increased from 50% to 68%. The onset of pistil growth occurred during the transition from bud swell to side green. Concomitantly, ~6°C of hardiness was lost during this period, yet these phenology stages were difficult to distinguish visually. Relative water content was strongly associated with pistil growth and served as an objective indicator of bud development.